The electron microscope has proven to be an integral factor in the research program of the Laboratory of Infectious Diseases in the arena of enteric viruses for over two decades. Its use, application and implementation in uncharted, novel areas of research led to seminal discoveries that resulted in the expansion and initiation of various programs. For example, using the technique of immune electron microscopy, LID scientists discovered (i) the Norwalk virus which was the first major viral etiologic agent of epidemic gastroenteritis and (ii) the hepatitis A virus. In addition, the first detection of human rotavirus (which was discovered in Australia) in the United States was made by electron microscopy by LID scientists. Because the Norwalk and related viruses still defy cultivation in any cell culture system, along with the recent expression of 27nm virus-like particles belonging to this group of agents, the electron microscope has experienced a resurgence of activity as it continues to serve a seminal role in the research program of the Epidemiology Section. It is the only method for (i) the direct detection of the 27 nm recombinant virus-like particles, as well as the native 27 nm virus particles and, (ii) the elucidation of antigenic relationships among these native viruses or recombinant virus-like particles. In addition, the electron microscope serves as an important adjunct to many of the studies of the section, providing information for laboratory, epidemiologic and clinical studies. The continued demand for electron microscopic support was again demonstrated by the 31 individual experiments that were conducted by electron microscopy since the previous annual report.